Selecting a Refractometer on Amazon.com

A refractometer is an instrument that uses light refraction to identify a sample, determine its purity, and measure the concentration of a particular substance in that sample. It may provide a reading of the refractive index (the ratio of the speed of light in empty space to the speed of light in a substance) or the specific gravity (the density of a substance relative to a reference substance) of a liquid or solid. While some refractometers measure more than one parameter, others are calibrated for a specific measurement such as sugar content, alcohol percentage, salinity, percent of solids, total proteins, and immunoglobulin levels. A salinity refractometer, for example, measures dissolved salt in a solution and is used to test seawater and maintain marine aquariums. One of the most common types of refractometer has a scale in degrees or percent Brix for readings of the sugar content in beer, wine, fruits, and vegetables.

Refractometers may be analog or digital. Analog models have a prism for refraction, an analog scale that is illuminated by ambient light, and an eyepiece for viewing the scale. A digital refractometer displays test results on an LED or LCD, removing the subjective element of the analog scale, and often has automatic temperature compensation (ATC) to provide consistent test results by correcting for variations in air and sample temperature. Refractometers are available as handheld, benchtop, and inline models. A handheld, portable refractometer enables use in a lab or in the field. Benchtop models, such as an Abbe refractometer, generally provide improved accuracy and repeatability for research and other high-precision applications. For continuous monitoring applications such as industrial process control, an inline refractometer may be selected.

The housing of a refractometer may be metal or plastic, and the best material to select may be determined by the samples being tested and the testing environment. For example, polybutylene terephthalate (PBT) plastic housing resists salty and acidic samples. Certain instruments are Ingress Protection (IP) rated for the degree of protection they offer against solid objects and water. Refractometers are used for quality control in food and beverage making and pharmaceuticals manufacturing; clinical analysis of urine, blood serum, and other biological fluids; evaluating gems and minerals in gemology and geology; testing coolants, oils, and metalworking fluids in industrial settings; and checking water quality in ecological applications.